Lubrication involves the process of friction reduction, accomplished by maintaining a film of a lubricant between two surfaces which are moving with respect to each other. The lubricant prevents contact of the moving surfaces, thus greatly lowering the coefficient of friction. Since lubricants for different uses operate under different conditions, numerous additives have been developed to establish or enhance various properties of lubricants. Representative types of additives which are used include viscosity improvers, detergents, dispersants, antioxidants, extreme pressure additives, corrosion inhibitors and others. Frequently, combinations of additives are required.
Of particular importance in many applications are antiwear agents, many of which function by a process of interaction with the surfaces, thereby providing a chemical film which prevents metal-to-metal contact under high load conditions. Wear inhibitors which are useful under extremely high load conditions are frequently called "extreme pressure agents". These extreme pressure agents are frequently selected from the following chemical types: zinc organodithiophosphates; sulfurized olefins, chlorinated waxes; amine salts of phosphate esters; phosphites; and others. Certain of these materials, however, must be used judiciously in certain applications due to their property of accelerating corrosion of metal parts, such as bearings. In addition, some applications require very low concentrations of certain elements, such as phosphorus, which restricts the utility of otherwise quite useful extreme pressure agents.
There are several commercially available products which are extreme pressure fluid additives. These would include a proprietary synthetic ester, offered by Gateway under the tradename Syn-ester. Examples of chlorine-free additives would include Keil's Klor-free 427, a blend of phosphate esters and sulfurized lard oil, Dover Chemicals's NCL-2, a blend of petroleum sulfonate, phosphorus acid, and a long chain amine, and Mayfree, offered by Mayco, a blend of sulfurized fat and phosphate esters. Other prior art synthetic ester lubricating oil compositions would include those described in U.S. Pat. No. 3,720,612, U.S. Pat. No. 3,585,137, U.S. Pat. No. 3,483,122 and U.S. Pat. No. 3,986,965.